Vancomycin is a a glycopeptide antibiotic with bacetiocidal effects on gram positive bacteria by interfering with cell wall synthesis. The necessity for monitoring of serum vancomycin concentrations (SVCs) has been recently noticed at many institutions because of concerns for its nephrotoxicity. We aimed to describe the SVCs monitoring in pediatric patients, in an effort to determine subtherapeutic or toxic levels. The medical records were reviewed for all patients older than 60 days of age admitted to the general or subspecialty services who received intravenous vancomycin at Children's Medical Hospital in Tehran, Iran between July 2003 and December 2005. Because pharmacokinetic parameters for children with cancer may be different, this group was evaluated separately. During the study, 167 infants and children without cancer and 42 patients with cancer; aged between 3 months to 17.5 years were treated with vancomycin for various infections. In children without cancer, peak SVCs were in an adequate therapeutic range for 93% of patients (8-55 microg/ml). For children with cancer, peak SVCs was lower than 10 microg/ml (10%), and trough values were lower than 5 microg/ml (21%). In conclusion, according to the results of this research, due to different pharmacokinetics of vancomycin in cancerous patients, the monitoring of vancomycin plasma concentrations is necessary for the best therapeutic antibacterial activities with a fewer occurrence of serious adverse effects.